Negatively tilted upper-tropospheric troughs are a synoptic weather pattern associated with the development of thunderstorms and severe weather, including extreme fire weather and tornadoes. While various case studies and some preliminary climatological analysis have been conducted in the past, a thorough investigation of the development of these synoptic features during extreme weather events has not yet been done in Australia or elsewhere. This study aimed to identify how often negatively tilted troughs occur and how often they are associated with extreme storms and fire weather.
The objectives of the project were to:
• identify the extent to which negatively tilted troughs are associated with recent extreme weather events across southeast Australia;
• assess the relationship between the occurrence of negatively tilted troughs and on-ground conditions such as elevated fire danger, high winds and/or dangerous thunderstorms;
• assess seasonality of negatively tilted troughs and any potential link with large-scale climate drivers such as the Southern Annular Mode (SAM) and Indian Ocean Dipole (IOD).
The major components of the project were:
• a review of previously documented cases of negatively tilted upper-tropospheric troughs associated with severe weather;
• a detailed case study of the role of a negatively tilted upper-tropospheric trough in the extreme fire weather during the January 2003 Canberra bushfires;
• a detailed case study of the role of a negatively tilted upper-tropospheric trough in the development of a tornado outbreak in Perth in July 2014;
• a climatology of negatively tilted upper-tropospheric troughs in southern Australia for the period 1990-2018 and their relationship with severe weather reported in the Bureau of Meteorology Severe Storms Archive.
Citation: Love P, Fox-Hughes P, Remenyi T, Earl N, Rollins D, Mocatta G & Harris R (2021) A characterisation of synoptic weather features often associated with extreme events in southeast Australia: Stage 1 – common features of recent events, Bushfire and Natural Hazards CRC, Melbourne.